Pictures drawn by Sage

These pictures and images were drawn by Sage.

p = Graphics()
for n in range(1,20):
  f = lambda x: sum([sin(x*3^i)/(2^i) for i in range(1,n)])
  p += plot(f,0,float(pi/3),plot_points=2000,rgbcolor=hue(n/20))

p.show(xmin=0, ymin=0,dpi=250)

cool pic 1

Mirrored balls in tachyon

t = Tachyon(camera_center=(8.5,5,5.5), look_at=(2,0,0), raydepth=6, xres=1500, yres=1500)
t.light((10,3,4), 1, (1,1,1))
t.texture('mirror', ambient=0.05, diffuse=0.05, specular=.9, opacity=0.9, color=(.8,.8,.8))
t.texture('grey', color=(.8,.8,.8), texfunc=7) ## try other values of texfunc too!
t.plane((0,0,0),(0,0,1),'grey')
t.sphere((4,-1,1), 1, 'mirror')
t.sphere((0,-1,1), 1, 'mirror')
t.sphere((2,-1,1), 0.5, 'mirror')
t.sphere((2,1,1), 0.5, 'mirror')
show(t)

cool ray tracing pic

Math art by Tom Boothby

# Author: Tom Boothby
# This is a remake of an old art piece I made in POVRay


t = Tachyon(xres=1000,yres=600, camera_center=(1,0,5), antialiasing=3)
t.light((4,3,2), 0.2, (1,1,1))
t.texture('t0', ambient=0.1, diffuse=0.9, specular=0.5, opacity=1.0, color=(1.0,1,1))
t.texture('t1', ambient=0.5, diffuse=0.5, specular=0.0, opacity=1.0, color=(0,0,0))
t.texture('t2', ambient=0.2, diffuse=0.7, specular=0, opacity=0.7, color=(.5,.5,.5))
t.texture('t3', ambient=.9, diffuse=5, specular=0,opacity=.1, color=(1,0,0))
t.sphere((1,0,0), 30, 't2')



k=0
for i in srange(-pi*10,0,.01):
  k += 1
  t.sphere((cos(i/10)-.1, sin(i/10)*cos(i), sin(i/10)*sin(i)), 0.1, 't0')
  t.sphere((cos(i/10) + 2.1, sin(i/10)*cos(i), sin(i/10)*sin(i)), 0.1, 't1')

t.show(verbose=1)

cool pic 2

Twisted cubic in tachyon

t = Tachyon(xres=512,yres=512, camera_center=(5,0,0))
t.light((4,3,2), 0.2, (1,1,1))
t.texture('t0', ambient=0.1, diffuse=0.9, specular=0.5, opacity=1.0, color=(1.0,0,0))
t.texture('t1', ambient=0.1, diffuse=0.9, specular=0.3, opacity=1.0, color=(0,1.0,0))
t.texture('t2', ambient=0.2, diffuse=0.7, specular=0.5, opacity=0.7, color=(0,0,1.0))
k=0
for i in srange(-5,1.5,0.1):
    k += 1
    t.sphere((i,i^2-0.5,i^3), 0.1, 't%s'%(k%3))

t.show()

cool pic 3

Reflections from four spheres in tachyon

t6 = Tachyon(camera_center=(0,-4,1), xres = 800, yres = 600, raydepth = 12, aspectratio=.75, antialiasing = True)
t6.light((0.02,0.012,0.001), 0.01, (1,0,0))
t6.light((0,0,10), 0.01, (0,0,1))
t6.texture('s', color = (.8,1,1), opacity = .9, specular = .95, diffuse = .3, ambient = 0.05)
t6.texture('p', color = (0,0,1), opacity = 1, specular = .2)
t6.sphere((-1,-.57735,-0.7071),1,'s')
t6.sphere((1,-.57735,-0.7071),1,'s')
t6.sphere((0,1.15465,-0.7071),1,'s')
t6.sphere((0,0,0.9259),1,'s')
t6.plane((0,0,-1.9259),(0,0,1),'p')
t6.show()

fourspheres.png

A cone inside a sphere

sage: u,v = var("u,v")
sage: p1 = parametric_plot3d([cos(u)*v, sin(u)*v, 3*v/2-1/3], (u, 0, 2*pi), (v, 0, 0.95),plot_points=[20,20])
sage: p2 = sphere((0,0,2/3), color='red', opacity=0.5, aspect_ratio=[1,1,1])
sage: show(p1+p2)

http://sage.math.washington.edu/home/wdj/art/cone-inside-sphere.jpg

A cylinder inside a cone

sage: u,v = var("u,v")
sage: p1 = parametric_plot3d([cos(u)*v, sin(u)*v, 3/2-3*v/2], (u, 0, 2*pi), (v, 0, 1.5), opacity = 0.5, plot_points=[20,20])
sage: p2 = parametric_plot3d([cos(u)/2, sin(u)/2, v-3/4], (u, 0, 2*pi), (v, 0, 3/2), plot_points=[20,20])
sage: show(p1+p2)

http://sage.math.washington.edu/home/wdj/art/cylinder-inside-cone.jpg

A hypotrochoid animation by Dean Moore

Hypotrochoid. Written by Dean Moore, February 2008

http://sage.math.washington.edu/home/wdj/art/hypotrochoid_R_equals_7,_r_equals_2,_d=3.gif

 x-coordinate: x = (R - r)*cos(t) + d*cos(((R - r)/r)*t)                       
 y-coordinate: y = (R - r)*sin(t) - d*sin(((R - r)/r)*t)                       

 x = (R + r)*cos(t) - d*cos(((R + r)/r)*t)                                                          
 y = (R + r)*sin(t) - d*sin(((R + r)/r)*t)                                     

To draw different graphs, vary that parameters *R* (fixed circle's radius), *r* (rotating circle's radius), and *d* (length of "bar" from rotating circle), below; other parameters may be tweaked at will.

Of some note, the *epitrochoid* is the "epicycle" curve of Ptolemaic system astronomy; one project is to animate some of the Ptolemaic system, but this is for the future.

Program commences:

#*****************************************************************************
#       Copyright (C) 2007 Dean Moore < [email protected] >
#
#  Distributed under the terms of the GNU General Public License (GPL)
#                  http://www.gnu.org/licenses/
#*****************************************************************************
# Parameters that define the image:

R = 5   # Fixed circle's radius.
r = 3   # Rotating circle's radius, rotates about fixed circle's radius; make
        # this negative to place rotating circle on outside.
d = 5   # Length of the "bar" extending from the center of the rotating circle.

step = 0.025    # Size of "step" in below loops; the smaller the step, the more
                # "frames" in the final "movie" & the better the image, but the
                # slower the program runs -- and the more bytes to the image.

figuresize = 4  # A constant, regulates size of final picture

delayBetweenImages = 0 # A constant, delay between images in final "movie."

colorOfFixedCircle    = (0, 0, 1) # Colors of final image,
colorOfRotatingCircle = (0, 1, 0) # all described by
colorOfCenterPoint    = (0, 0, 0) # names.
colorOfBar            = (0, 0, 0)
colorOfCurve          = (1, 0, 0)

thicknessOfFixedCircle            =  1   # Thickness of "fixed" circle that never moves.
thicknessOfRotatingCircle         =  1   # Thickness of circle that rotates.
thicknessOfCenterOfRotatingCircle = 15   # Size of small circle's center.
thicknessOfBar                    =  1   # Thickness of "bar" from rotating circle.
penSize                           = 10   # Size of "pen" at end of the "bar."
thicknessOfCurve                  =  0.5 # Thickness of final curve, really a lot of line segments.

# End of parameters user can realistically vary.

origin = (0, 0) # Maybe irrelevant, but NO MAGIC NUMBERS!!  See
                # < http://en.wikipedia.org/wiki/Magic_number_(programming) >.
                # Comes from my days as a C/C++ programmer.

# Graphic parameters, defined here:

L = Graphics() # Graphics for the curve -- really a lot of segments of straight
               # lines.  If the image looks choppy, drop variable *step* above.

v = []         # Holds the curve from *L*, later converted to variable *curve*.

# More parameters, all of which are defined by earlier parameters:

rDiff = (R-r)              # The rotating circle may exceed fixed circle;
                           # values may be negative, so we may have a
                           # negative value.  We use this so much, we give
                           # it a name.

sizeOfGraph = max(R, abs(r) + abs(d), abs(R) - (r) + abs(d)) # Big as it can get -- may be
                                                             # a liberal estimate.

circle2PI = (abs(rDiff)/r).denom() # Number of rotations about 2*pi.  It
                                   # takes a bit of thought, but see the above
                                   # parametric equations.  An example is best:
                                   # picture R=8, r=6.  We have
                                   # (rDiff)/r = (8-6)/6 = 2/6 = 1/3, reduced. For
                                   # the argument *((rDiff)/r)t* to get back to 2*pi
                                   # (i.e., zero) in cos(((R - r)/r)t) & sin(((R - r)/r)t),
                                   # we need to go 2*(3*pi).  A pen & paper & some
                                   # scribbling makes this easy, be it this not
                                   # clear.  The *abs* is probably irrelevant.

limit =  ceil(2*circle2PI/step)    # Loop about circle this many times, by *step*.
                                   # Parameter *circle2PI* never is again used.  Factor
                                   # of 2 is unavoidable, circle 2*pi; see below loops.

First: I use the same trig functions, over an over again. Why re-invent the wheel & waste computer time? Put the needed trig functions in arrays & "recycle" them as needed.

sin1 = [ 0 for i in range(limit) ] # First
sin2 = [ 0 for i in range(limit) ] # define
cos1 = [ 0 for i in range(limit) ] # arrays, ...
cos2 = [ 0 for i in range(limit) ]

increment = 0 # Adding a bunch of numbers is more efficient than multiplying
              # *i*pi*step, but it is a trivial difference.

multiplier = pi*rDiff/r # Efficiency!  Don't repeat the same math
                        # countless times.

for i in srange(limit): # Note above definition of parameter *limit*, the
                        # factor of 2, and the below trig functions.  All
                        # this program's loops go *limit*.

    sin1[i] = sin(increment*pi)         # Now fill
    cos1[i] = cos(increment*pi)         # arrays
    sin2[i] = sin(increment*multiplier) # with our trig
    cos2[i] = cos(increment*multiplier) # functions.

    increment += step                   # End *i*-loop.

The next are described by names, but a few notes:

I animated it, as that makes it appear in all frames. It never moves.

circle at *rDiff* from the edge of the fixed circle; its radius is *r*, and it rotates about the fixed circle a total of *circle2PI* times. Find any internet reference on these curves to see it.

a clear center.

that follows its rotation around the fixed circle. It always emanates from the same center as *fixedCircle*, -- see *fixedCircle* documentation, above -- and its terminal point comes from the parametric equation of a hypotrochoid (top).

of the same color as the final curve. Note it is at the same point as the terminal point of the "bar."

fixedCircle     = animate([circle(origin, R,          # Centered at origin, radius *R*.
                           rgbcolor=colorOfFixedCircle,
                           thickness = thicknessOfFixedCircle)
                           for i in srange(limit)            # Animating loop.
                          ],
                           xmin=-sizeOfGraph, ymin=-sizeOfGraph,
                           xmax= sizeOfGraph, ymax= sizeOfGraph,
                           figsize=[figuresize, figuresize])

rotatingCircle  = animate([circle((rDiff*cos1[i],rDiff*sin1[i]), r, # Note center, radius *r*
                           thickness = thicknessOfRotatingCircle,
                           rgbcolor=colorOfRotatingCircle)
                           for i in srange(limit)        # Animating loop
                          ],
                           xmin=-sizeOfGraph, ymin=-sizeOfGraph,
                           xmax= sizeOfGraph, ymax= sizeOfGraph,
                           figsize=[figuresize,figuresize])

centerPoints    = animate([point((rDiff*cos1[i],rDiff*sin1[i]), # Center of *fixedCircle*.
                           rgbcolor=colorOfCenterPoint,
                           pointsize=thicknessOfCenterOfRotatingCircle)
                           for i in srange(limit)                      # Animating loop
                          ],
                           xmin=-sizeOfGraph, ymin=-sizeOfGraph,
                           xmax= sizeOfGraph, ymax= sizeOfGraph,
                           figsize=[figuresize,figuresize])

bar             = animate(line([(rDiff*cos1[i], rDiff*sin1[i]), # Starts here, and ...
                                (d*cos2[i] + rDiff*cos1[i],     # Ends at
                                  rDiff*sin1[i] - d*sin2[i])    # this point.
                               ],
                           thickness = thicknessOfBar,
                           rgbcolor=colorOfBar)
                           for i in srange(limit))               # Animating loop

pointAtPen      = animate([point((d*cos2[i]+rDiff*cos1[i],     # End of pen, same x & y
                                 (rDiff)*sin1[i] - d*sin2[i]), # coordinates as endpoints of *bar*
                           rgbcolor=colorOfCurve, 
                           pointsize=penSize)
                           for i in srange(limit)                   # Animating loop
                           ],
                           xmin=-sizeOfGraph, ymin=-sizeOfGraph,
                           xmax= sizeOfGraph, ymax= sizeOfGraph,
                           figsize=[figuresize,figuresize])

# Prepare to draw the curve; we use four "important" variables: x0, x1, y0 & y1;
# the line segment goes from (x0, y0) to (x1, y1):

x0 = rDiff + d     # Initial values of these variables; bumped up at bottom
                   # of next loop -- see a graph or look at parametric equations
                   # at zero to understand why it has this value.

y0 = 0             # The "pen" out the small circle starts at this (x0, y0).

# Now to compute the curve, in the next loop.  Starts at zero, even if
# this seems to make the first a junk computation; otherwise the output
# looks weird:

for i in srange(limit): # Parameter *circle2PI* is number of times we rotate
                        # the "fixed" circle; limit=2*circle2PI; see above
                        # documentation.

    x1 = rDiff*cos1[i] + d*cos2[i]   # Initial, starting point of
                                    # the line; see parametric
                                    # equations.

    y1 = rDiff*sin1[i] - d*sin2[i] # Again, see the parametric
                                  # equation at top.
    # Now make the line:

    L += line([(x0, y0),(x1, y1)], rgbcolor = colorOfCurve , thickness=thicknessOfCurve)

    L.xmin(-sizeOfGraph)  # Some nonsense
    L.ymin(-sizeOfGraph)  # that needs done.
    L.xmax( sizeOfGraph)
    L.ymax( sizeOfGraph)

    x0 = x1 # Bump up these variables, start of
    y0 = y1 # next line segment is end of last.

    v.append(L) # *** End of loop ***
               # Stash curve *L* in the variable *v*.

curve = animate(v) # Animate the curve, and ...

# Show the entire "movie":

(fixedCircle + rotatingCircle + pointAtPen + bar + centerPoints + curve).show(delay=delayBetweenImages)

We've shown the final image; done with program.

A simpler hypotrochoid

The following animates a hypotrochoid much to the same effect as the previous script, but much more concisely.

import operator

# The colors for various elements of the plot:
class color:
    stylus = (1, 0, 0)
    outer  = (.8, .8, .8)
    inner  = (0, 0, 1)
    plot   = (0, 0, 0)
    center = (0, 0, 0)
    tip    = (1, 0, 0)
# and the corresponding line weights:
class weight:
    stylus = 1
    outer  = 1
    inner  = 1
    plot   = 1
    center = 5
    tip    = 5

scale = 1            # The scale of the image
animation_delay = .1 # The delay between frames, in seconds

# Starting and ending t values
t_i = 0
t_f = 2*pi
# The t values of the animation frames
tvals = srange(t_i, t_f, (t_f-t_i)/60)

r_o = 8 # Outer circle radius
r_i = 2 # Inner circle radius
r_s = 3 # Stylus radius

# Coordinates of the center of the inner circle
x_c = lambda t: (r_o - r_i)*cos(t)
y_c = lambda t: (r_o - r_i)*sin(t)

# Parametric coordinates for the plot
x = lambda t: x_c(t) + r_s*cos(t*(r_o/r_i))
y = lambda t: y_c(t) - r_s*sin(t*(r_o/r_i))

# Maximum x and y values of the plot
x_max = r_o - r_i + r_s
y_max = find_maximum_on_interval(y, t_i, t_f)[0]

# The plots of the individual elements. Order is important; plots
# are stacked from bottom to top as they appear.
elements = (
    # The outer circle
    lambda t_f: circle((0, 0),               r_o, rgbcolor=color.outer, thickness=weight.outer),
    # The plot itself
    lambda t_f: parametric_plot((x, y), t_i, t_f, rgbcolor=color.plot,  thickness=weight.plot),
    # The inner circle
    lambda t_f: circle((x_c(t_f), y_c(t_f)), r_i, rgbcolor=color.inner, thickness=weight.inner),
    # The inner circle's center
    lambda t_f: point((x_c(t_f), y_c(t_f)),       rgbcolor=color.center,pointsize=weight.center),
    # The stylus
    lambda t_f: line([(x_c(t_f), y_c(t_f)), (x(t_f), y(t_f))], rgbcolor=color.stylus, thickness=weight.stylus),
    # The stylus' tip
    lambda t_f: point((x_c(t_f), y_c(t_f)),       rgbcolor=color.tip,   pointsize=weight.tip),
)

# Create the plots and animate them. The animate function renders an
# animated gif from the frames provided as its first argument.
# Though avid python programmers will find the syntax clear, an
# explanation is provided for novices.
animation = animate([reduce(operator.add, (f(t) for f in elements))
                     for t in tvals],
                    xmin=-x_max, xmax=x_max,
                    ymin=-y_max, ymax=y_max,
                    figsize=(x_max*scale, y_max*scale * y_max/x_max))

animation.show(delay=animation_delay)

# The previous could be expressed more pedagogically as follows:
#
#   Evaluate each function in the elements array for the provided t
#   value:
#
#     plots = lambda t: f(t) for f in elements
#
#   Join a group of plots together to form a single plot:
#
#     def join_plots(plots):
#         result = plots[0]
#         for plot in plots[1:]:
#             result += plot
#         return result
#
#   or
#
#     add = lambda a, b: a + b
#     join_plots = lambda plots: reduce(add, plots)
#
#   Create an array of plots, one for each provided t value:
#
#     frames = [join_plots(plots(t)) for t in tvals]
#
#   Finally, animate the frames:
#
#     animation = animate(frames)

The witch of Maria Agnesi

by Marshall Hampton {{{xtreme = 4.1 myaxes = line(-xtreme,0],[xtreme,0,rgbcolor = (0,0,0)) myaxes = myaxes + line(0,-1],[0,2.1,rgbcolor = (0,0,0)) a = 1.0 t = var('t') npi = RDF(pi) def agnesi(theta): mac = circle((0,a),a,rgbcolor = (0,0,0)) maL = line(-xtreme,2*a],[xtreme,2*a) maL2 = line(0,0],[2*a*cot(theta),2*a) p1 = [2*a*cot(theta),2*a*sin(theta)^2] p2 = [2*a*cot(theta)-cot(theta)*(2*a-2*a*sin(theta)2),2*a*sin(theta)2] maL3 = line([p2,p1,[2*a*cot(theta),2*a]], rgbcolor = (1,0,0)) map1 = point(p1) map2 = point(p2) am = line(-.05,a],[.05,a, rgbcolor = (0,0,0)) at = text('a',[-.1,a], rgbcolor = (0,0,0)) yt = text('y',[0,2.2], rgbcolor = (0,0,0)) xt = text('x',[xtreme + .1,-.1], rgbcolor = (0,0,0)) #tt = text('t',[.15,.1], rgbcolor = (0,0,0)) matext = at+yt+xt ma = mac+myaxes+maL+am+matext+maL2+map1+maL3+map2 return ma

def witchy(theta): ma = agnesi(theta) agplot = parametric_plot([2*a*cot(t),2*a*sin(t)^2],[t,.001,theta], rgbcolor = (1,0,1)) return ma+agplot

a2 = animate([witchy(i) for i in srange(.1,npi-.1,npi/60)]+[witchy(i) for i in srange(npi-.1,.1,-npi/60)], xmin = -3, xmax = 3, ymin = 0, ymax = 2.3, figsize = [6,2.3], axes = False)

a2.show() }}} [ATTACH]

http://sage.math.washington.edu/home/wdj/art/padic-seasons-greetings.png

This is the code:

sage: P1 = Zp(3).plot(rgbcolor=(0,1,0))
sage: P2 = Zp(7).plot(rgbcolor=(1,0,0))
sage: P3 = text("$Seasons$ $Greetings$ ",(0.0,1.8))
sage: P4 = text("$from$ $everyone$ $at$ sagemath.org!",(0.1,-1.6))
sage: (P1+P2+P3+P4).show(axes=False)

Lorentz butterfly

"""
Draws Loretz butterfly using matplotlib (2d) or jmol (3d).
Written by Matthew Miller and William Stein.

"""

def butterfly2d():
    """"
    EXAMPLE:
        sage: butterfly2d()
    """    
    g = Graphics()
    x1, y1 = 0, 0
    from math import sin, cos, exp, pi
    for theta in srange( 0, 10*pi, 0.01 ):
        r = exp(cos(theta)) - 2*cos(4*theta) + sin(theta/12)^5
        x = r * cos(theta)  # Convert polar to rectangular coordinates
        y = r * sin(theta)
        xx = x*6 + 25       # Scale factors to enlarge and center the curve.
        yy = y*6 + 25
        if theta != 0: 
            l = line( [(x1, y1), (xx, yy)], rgbcolor=hue(theta/7 + 4) )
            g = g + l
            x1, y1 = xx, yy
    g.show(dpi=100, axes=False)

def butterfly3d():
    """"
    EXAMPLE:
        sage: butterfly3d()
    """    
    g = point3d((0,0,0))
    x1, y1 = 0, 0
    from math import sin, cos, exp, pi
    for theta in srange( 0, 10*pi, 0.05):
        r = exp(cos(theta)) - 2*cos(4*theta) + sin(theta/12)^5
        x = r * cos(theta)  # Convert polar to rectangular coordinates
        y = r * sin(theta)
        xx = x*6 + 25       # Scale factors to enlarge and center the curve.
        yy = y*6 + 25
        if theta != 0:
            l = line3d( [(x1, y1, theta), (xx, yy, theta)],
            rgbcolor=hue(theta/7 + 4) )
            g = g + l
            x1, y1 = xx, yy
    g.show(dpi=100, axes=False)

http://sage.math.washington.edu/home/wdj/art/butterfly2d.png

http://sage.math.washington.edu/home/wdj/art/butterfly3d.png

"three famous plots of chaos" by Pablo Angulo

# Author: Pablo Angulo

Posted to sage-devel 2008-09-13. See also https://sage.math.washington.edu:8101/home/pub/3
-----------------------------------

#Plots Feigenbaum diagram: divides the parameter interval [2,4] for mu
#into N steps. For each value of the parameter, iterate the discrete
#dynamical system x->mu*x*(1-x), drop the first M1 points in the orbit
#and plot the next M2 points in a (mu,x) diagram

N=200
M1=200
M2=200
x0=0.509434

puntos=[]
for t in range(N):
   mu=2.0+2.0*t/N
   x=x0
   for i in range(M1):
       x=mu*x*(1-x)
   for i in range(M2):
       x=mu*x*(1-x)
       puntos.append((mu,x))
point(puntos,pointsize=1)

---------------------------------------
#Lorentz attractor
#plots the orbit of the point (1,1,1) using the simplest euler method

h=0.01;         # time step
k=2000          # number of iterations (time k*h will be reached)

sigma=10;       #parameters
rho=28;
beta=8/3;

x=1; y=1; z=1;              # initial data

puntos=[]
for i in range(k):
   x,y,z=x+h*( sigma*(y-x) ), y+h*( x*(rho - z) - y ), z+h*( x*y - beta*z )
   puntos.append((x,y,z))
point3d(puntos)

--------------------------------------------

#Mandelbrot set: the final plot is a subset of the complex plane;
#the color at point c is porportional to the number of iterations that
#the discrete dynamical system z->z^2+c takes to leave a circle around
#the origin when z0=0

N=100        #resolution of the plot
L=50        #limits the number of iterations
x0=-2; x1=1; y0=-1.5; y1=1.5  #boundary of the region plotted
R=3        #stop after leaving the circle of radius R

m=matrix(N,N)
for i in range(N):
   for k in range(N):
       c=complex(x0+i*(x1-x0)/N, y0+k*(y1-y0)/N)
       z=0
       h=0
       while (h<L) and (abs(z)<R):
           z=z*z+c
           h+=1
       m[i,k]=h
matrix_plot(m)

def sierpinski_seasons_greetings():
    """
    Code by Marshall Hampton.
    Colors by David Joyner.
    General depth by Rob Beezer.
    Copyright Marshall Hampton 2008, licensed
    creative commons, attribution share-alike.
    """
    depth = 7
    nsq = RR(3^(1/2))/2.0
    tlist_old = [[[-1/2.0,0.0],[1/2.0,0.0],[0.0,nsq]]]
    tlist_new = [x for x in tlist_old]
    for ind in range(depth):
       for tri in tlist_old:
           for p in tri:
               new_tri = [[(p[0]+x[0])/2.0, (p[1]+x[1])/2.0] for x in tri]
               tlist_new.append(new_tri)
       tlist_old = [x for x in tlist_new]
    T = tlist_old
    N  = 4^depth
    N1 = N - 3^depth
    q1 = sum([line(T[i]+[T[i][0]], rgbcolor = (0,1,0)) for i in range(N1)])
    q2 = sum([line(T[i]+[T[i][0]], rgbcolor = (1,0,0)) for i in range(N1,N)])
    show(q2+q1, figsize = [6,6*nsq], axes = False)

GIMP was used to add a Season's greetings message:

http://sage.math.washington.edu/home/wdj/art/sierpinski-seasons-greetings-from-sage.png

Also (thanks to Rob Beezer) available in poster form in pdf format: http://sage.math.washington.edu/home/wdj/art/seasons-greetings-sage.pdf, and in A4 size: http://sage.math.washington.edu/home/wdj/art/seasons-greetings-sage-a4.pdf.